Reference electrode assembly



April 1964 E. P. ANDERSON ETAL 3,129,161

REFERENCE ELECTRODE ASSEMBLY Filed Oct. 10, 1958 SILVER 2 SILVER 4 CHLORIDE INVENTORS.

EDWARD R ANDERSON ARTHUR J. ZWANZ IG KM [Aw ATTO EYS United States Patent 3,129,161 REFERENCE ELECTRODE ASSEMBLY Edward P. Anderson, Livingston, and Arthur J. Zwanzig,

Madison, N.J., assignors, by mesne assignments, to

Engelhard Industries, Inc, Newark, NJ., a corporation of Delaware Filed Oct. 10, 1958, Ser. No. 766,462 1 Claim. (Cl. 204-196) This invention relates to a reference electrode assembly for use in cathodic protection systems for metallic surfaces in contact with an electrolyte, and is especially intended for such systems installed on a ship.

Most corrosion in aqueous solutions behaves similarly to a battery. Due to metallurgical differences in the steel plating, certain areas of the steel act as the noble side of a battery and are called cathodes while other areas become the active side and are called anodes. In a suitable electrolyte, such as sea water, current will flow within suchta local battery.

Protection against corrosion is achieved by changing the potentials surrounding these small local anodic and cathodic areas and, upon applying current from an external anode, the local anodic and cathodic areas of the ship hull will all become cathodic with respect to the sea water. When this condition is attained, theoretically all local corrosion will cease.

While insuflicient potentials do not protect the hull against corrosion to the desired extent, excessive current damages the painted areas of the hull and therefore an optimum exists which is known to be subject to fluctuations. This optimum being a function of the degree of polarization of the immersed surface, it is customary to determine the polarization by means of a reference cell which is actually a half cell consisting of a single electrode. When immersed in the electrolyte, a potential difference between the half cell and the polarized surface is generated and the produced current is used to control the power supply to the anodes of the cathodic protection system, as described in copending application Serial No. 513,111 filed June 6, 1955, now U.S. Patent 2,844,935.

Reference electrodes for this purpose have been suggested which consist of a silver wire screen impregnated with precipitated silver chloride and, since such a structure has little mechanical resistance, it has been found necessary to mount the screen electrode in a protective housing, as described in copending application Serial No. 728,733, filed April 15, 1958, now U.S. Patent No. 2,934,484, granted April 26, 1960.

This invention eliminates such protective devices and provides a mechanically resistant reference electrode which can be readily mounted in the hull of a ship, for example, by means of a packing gland similar to that used for mounting the anodes of a cathodic protection system on a ship and described in copending application Serial No. 778,374, filed December 5, 1958, now U.S. Patent 3,075,911.

In accordance with the invention, the reference electrode assembly comprises a body portion of silver, coated with silver chloride, secured to and insulated from the hull of a ship and connected into the control circuit of a cathodic protection system. Preferably, a rivet-shaped body portion is used, having a head and a stem thereon, whereby the slightly curved surface of the head serves as the useful contacting surface of the electrode while the stem extends through the hull and is sealed thereto by means of a packing gland.

The invention will be further illustrated by reference to the accompanying drawing in which one embodiment of the invention is illustrated in a sectional view.

The rivet-shaped electrode body consists of a slightly curved head 2 made from silver, the curved portion thereof forming the surface adapted to contact with water and being covered with a layer 4 of silver chloride. The head 2 is provided with a metallic stem 6 made from stainless steel, brass or the like and having the end portion 8 thereof, of smaller diameter, extending into a packing gland 10, the gland being welded in a bore in the hull 12.

The packing gland 10 has a circular shoulder 14 machined therein, the annular space formed between the stem 6 and the wall of the gland being filled with a conventional packing material 16, e.g., tetrafluoroethylene. An annular, internally threaded jam nut 18, cooperating with an external thread on the stem portion 8 serves to compress the packing material 16, preferably over an insulating, annular washer 20 mounted between the packing 16 and the jam nut 18. Since the washer 20 extends into the gland 10 and since the outer diameter of the jam nut 18 is smaller than the inner diameter of the gland 10, the jam nut is maintained spaced and insulated from the gland. Electrical connection with the control circuit of the system on a ship is provided by a connector pin 22 axially secured in a bore in the stem portion 8-. A bushing 24 completes the insulation of the stem 6 from the gland portion between the shoulder 14 and the head 2.

Compression of the packing 16 is obtained by tightening the jam nut 18. Simultaneously, the head 2, together with an insulating washer 26 of neoprene, for example, is forced against the hull to form a water-tight seal.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

In a cathodic protection system for ships, the hull of the ship, a reference electrode including a solid, integral rivetshaped body portion having a metallic stem and a head with a continuous silver surface secured to said stem, a coating of silver chloride on said head, a cylindrical packing gland mounted in a bore in the hull to protrude inwardly into the ship, said stem extending through said gland, insulating packing means arranged between said stem and said packing gland, means for compressing said packing means, and an electrical connector secured to said stem.

References Cited in the file of this patent UNITED STATES PATENTS 2,697,070 Arthur Dec. 14, 1954 2,733,201 Thompson Ian. 31, 1956 2,822,324 Gaylor et al. Feb. 4, 1958 2,910,420 Preiser Oct. 27, 1959 2,930,967 Laird et al. Mar. 29, 1960 

